Wood barrels have been widely used in the wine making industry for wine storage, transportation, and more importantly adding wood-derived complexities to the wine during the process (i.e. aging process). Aging alcoholic fluids in wood barrels undergo slow but complicated physical, chemical, and biological reactions which involve alcoholic fluids penetrating into the barrel wood, extracting soluble wood-derived compounds (wood-phenols and other volatile compounds) from the barrel, partially degrading wood barrel to further release wood-derived compounds, reacting of those compounds with compounds in spirits/beverages, the oxidation of components in spirits/beverages, and so forth. The overall aging process modifies spirits/beverages with appearance, smell, taste and other quality complexities. The barrel aging process depends largely on the barrel characteristics and takes years to achieve desirable flavors imparted by the wood barrels due to the fact that only a small percentage of wood barrel area contacts and reacts with the spirits/beverages. The wood staves are fire toasted prior to barrel cooperage or the barrel is fire toasted post cooperage, which leads to partial or total loss of certain wood flavors by the toasting process. Major drawbacks of wood barrel aging also include: the high cost of barrels and their maintenance, the loss of spirits/beverages by evaporation over the long aging duration, the risk of barrel leakage destroying the quality of spirits/beverages prior to the maturation, the risk of possible microorganism contamination during the aging process, and the large long-term inventory in stock. Therefore, an accelerated spirit/beverage aging method and/or system is demanded.
Accelerating spirit/beverage aging using wood materials depends on: 1) the availability and accessibility of wood-derived compounds; and 2) the reaction kinetics of the wood-derived compounds with the spirit/beverage. The accessibility to wood derived compounds depends on the direct contact of spirit/beverage with wood surfaces, the penetration of spirit/beverage into wood, and the diffusion of wood-derived compounds out of the wood into the spirits/beverages. In this aspect, the spirit/beverage contacting surface area and the open structure of the wood are critical. The larger surface area and more open porous structure increase the accessibility of reactants from the wood. The reaction kinetics is mainly impacted by the aging conditions including temperature, pressure, oxygen content, and the movement of spirits/beverages. A few patents disclosed methods to accelerate wine aging by either increasing the wood/spirit interaction area and/or improving the reaction conditions.
Wood fragments (plugs, dowels, rods, shavings, particles, granules, slabs, etc.) have been used as alternatives to barrel aging for spirits/beverages (U.S. Pat. Nos. 2,108,661, 2,203,229, 3,942,423, 4,350,708, 4,173,656, 4,956,194, 6,378,419). Compared to barrel aging, the use of wood fragments has larger spirit-wood contact area. Once the wood fragments are added to the spirits or beverages, the wood-phenols and other volatile compounds are absorbed by the spirits or beverages in the same manner as they are when in the wood barrel. With that, no costing wood barrel is required for aging. The spirit/beverage can be aged in any containers such as stainless steel, glass, plastic or used wood barrel. The entire process costs much less and goes to completion faster than the traditional wood barrel aging technique. It is noted, however, spirit/beverage aging using wood fragments is only able to achieve short term results since the reaction rate is not accelerated significantly due to the facts that the increase of surface area is macroscopic by physically reducing the wood dimensions and that the spirit/beverage is always saturated compared to the wood-derived compounds. Faster soak time also does not permit time dependent reactions of continuously released wood derived compounds from the barrel. In addition, the preparation of wood fragments (such as grinding or mechanical treatment) may damage the wood structures and lead to the partial loss or the distribution alteration of wood-derived compounds which can lead to off flavors. In addition, the fire toasting of small wood fragments is challenging to achieve desired and consistent flavor profiles.
U.S. Pat. No. 9,212,343 disclosed an apparatus with arrays of closely-spaced holes or cross-grain grooves on the inside of a wood barrel surface. With such a design, the exposure area was increased and the aging of liquids in such barrels could be accelerated. This method requires customized fabrication of barrel. The integrity and mechanical strength of barrel are weakened due to the holes or grooves.
U.S. Pat. No. 4,350,708 disclosed an accelerated process for aging an alcoholic beverage using aroma extracts from oak shavings. The oak shavings were extracted with alcohol-water to prepare first extract and demineralized water to prepare second extract. Two extracts were mixed and combined with alcoholic beverages to obtain aged flavors. The extraction and addition method cannot guarantee a full naturally balanced spectrum of wood-derived compounds reacted with alcoholic beverage for aging purposes. Therefore, the ultimate quality of alcoholic liquids from this aging method may not as good as the natural barrel-aged ones.
During the barrel-aging of spirits, some studies show linear increase of ethyl acetate over the entire aging time. Esterification is therefore considered one of the indicators for the spirit maturation and aging. Acceleration of esterification has been disclosed in a few patents and patent applications as methods of accelerating spirit aging. U.S. Pat. No. 6,869,630 disclosed an aging method of adding ethyl acetate to raw beverage prior to the aging process. US Pat. Appl. 20090291175 disclosed a method of using esterification catalysts for aging alcoholic liquids. Since esterification is only one of the numerous and complicated reactions occurred in the natural barrel-aging processes, a full spectrum of quality complexities cannot be obtained by only accelerating the esterification. The flavor of such aged beverages goes off flavor and is not equivalent to the natural barrel aged ones. Esterification process for spirit aging is essentially a chemical adulteration designed to meet the chemical analysis specifications.
U.S. Pat. No. 7,762,179 disclosed a system and a method which employs a device internally or externally to induce the motion of spirit or wine in wood barrel during the aging process. The increase in movement and circulation of wine is believed to accelerate the aging process to some extent. Speeding up reaction kinetics by this approach can lead to deleterious consequences i.e. off flavors.
Other aging acceleration methods include increasing oxygen inputs from hollow tube design as disclosed in U.S. Pat. No. 6,966,250, heating the aging alcoholic liquids up to 200° C. as disclosed in U.S. Pat. No. 6,869,630, and accelerating oxidation-reduction of wines using a silver/gold/copper alloy element as disclosed U.S. Pat. No. 7,571,673. All these aging acceleration methods don't achieve the same ultimate quality as the natural barrel aging process at the end.
With above disclosed methods for accelerated aging of wines and spirits, the ultimate quality of aged liquids is still not comparable to the natural barrel aging. An accelerated aging method or system which can age spirits/beverages equivalent to or better than the natural barrel aging process is wanted. In this present invention, innovative methods are disclosed to age spirits/beverages using activated wood materials and/or naturally flavored impregnated wood materials under a subcritical/critical/supercritical carbon dioxide environment. The method preserves the natural wood structures, increase the surface area both micro- and macroscopically, and imparts the full spectrum of natural wood flavors to spirits/beverages under a controlled and accelerated manner. The net result is equivalent to or better than and not contrary to the standard natural barrel aging process.
The wood materials can be activated with subcritical/critical/supercritical CO2 processing. Activated wood materials can then be added to liquid under ambient, pressure, vacuum, and/or subcritical/critical/supercritical CO2 environments. Fruits, vegetables, herbs, and other such natural products can also be added to the wood materials to impregnate the activated wood with naturally flavors, vitamins, minerals, therapeutics, and other nutrients, Impregnated wood materials can then be combined with liquid and treated with subcritical/critical/supercritical CO2.